A British man serving a life sentence in the US for shooting his wife and baby daughter is to launch an appeal against his murder convictions.

Neil Entwistle, 32, originally from Worksop, was jailed in June 2008 for shooting his American wife, Rachel, 27, and their nine-month-old daughter, Lillian, in Hopkinton, Massachusetts, on 20 January 2006.

Entwistle's lawyer, Stephen Paul Maidman, will argue for a new trial at the Massachusetts supreme judicial court, the state's highest court. A decision could take weeks or even months to come through, a clerk at the court said.

In an appeal brief filed to the court, Maidman argues that evidence taken from the couple's rented home was seized illegally because police did not have the right to search the house without a warrant. He says the judge should have suppressed this evidence during Entwistle's trial.

"The two warrantless entries into the defendant's house by the police violated the federal and state constitutions.

"On the two occasions when the police entered the defendant's house, the police did not have objective knowledge of an emergency inside the house or have objective knowledge that there was a person inside the home in need of immediate aid," Maidman argues in the brief.

"The inevitable discovery doctrine does not purge the taint on the evidence seized as a direct result of these unlawful searches or the taint on the evidence derived from these unlawful searches. All of this evidence should have been suppressed at the defendant's trial."

But prosecutors have said police were justified in entering the property because they were responding to concerns about the family's wellbeing raised by friends and relatives. They say Entwistle had become despondent after accumulating tens of thousands of dollars of debt and had complained about his sex life with his wife.

Entwistle's lawyer also argues that Judge Diane Kottmyer did not thoroughly question potential jurors to determine whether they were biased against him after the case received intense local and international news coverage.

"That there was extraordinary prejudicial pre-trial publicity in this case that was both saturating and inflammatory, by Massachusetts and even national standards, cannot be legitimately disputed," Maidman wrote in the appeal brief. Kottmyer denied Entwistle's request to move the trial out of Middlesex county.

"The defendant is entitled to a new trial utilising a jury selection process where there can be no question that the seated jurors are fair and impartial," Mr Maidman writes.

Middlesex district attorney Gerard Leone, whose office prosecuted Entwistle, said he received a "true and just" trial.

Entwistle, a former IT consultant from Kilton, Worksop, left the US the day after the killings and told police he had departed because he wanted to be consoled by his parents in the UK. He said he found his wife and daughter cuddled together in bed, dead of apparent gunshot wounds, after he returned home from running errands.

Friends giving evidence said the couple appeared to have had a happy marriage and were both thrilled with their daughter.

Entwistle met his wife, from Kingston, Massachusetts, at college in England in 1999. The couple lived in England for a while after their daughter's birth, then moved to the US.

He was sentenced to life imprisonment without the possibility of parole at Middlesex County superior court in Woburn, Massachusetts, with the judge calling Entwistle's crimes "incomprehensible". Kottmyer imposed a 10-year probation sentence for two firearms offences and ordered that Entwistle should not profit from his crimes by writing a book.